This invention relates generally to turbine engines, and more particularly, to composite fan containment cases used with turbine engines.
Gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air which is mixed with fuel and channeled to the combustor. The mixture is then ignited and generates hot combustion gases. The combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
When engines operate in various conditions, foreign objects may be ingested into the engine. More specifically, various types of foreign objects, such as, but not limited to, large birds, hailstones, sand and/or rain, may be entrained into the inlet of a gas turbine engine. Foreign objects may impact a blade resulting in a portion of the impacted blade being damaged and/or torn loose from a rotor. Such a condition, known as foreign object damage (FOD), may cause the damaged rotor blade to pierce the surrounding engine casing which may result in cracks along an exterior surface of the engine casing, and/or possible injury to nearby personnel. Additionally, the foreign object damage may cause a portion of the engine to bulge or deflect resulting in increased stresses along the entire engine casing.
To facilitate preventing the increased engine stresses and the possible injury to personnel during an FOD event, at least some known engines are assembled with a metallic casing shell that increases the radial and axial stiffness of the engine, and that reduces stresses near the engine casing penetration. However, such casing shells are generally fabricated from a metallic material which increases the overall weight of the engine.
The high specific strength and stiffness of polymeric composite materials offer attractive weight reduction benefits for jet engine components. The majority of current composite components are fabricated with material in a unidirectional tape or woven fabric form. The required properties needed for a specific component are obtained by assembling many layers of the chosen tape or woven fabric into one monolithic shell.
Known methods of fabricating composite fan cases with dry fiber preform may include fiber preforming and preform wrapping, and then resin infusion and curing. Known composite fan cases may also be fabricated with prepreg preform in a similar wrapping process. However, using known methods of fabricating composite fan cases, dry or prepreg fiber preforms must be formed with the same shape as the fan case. Hence, they are also known as conforming fiber preforms. To shape the fiber preforms with the same shape as the fan case, preform take-up spools and the wrapping mandrel, or curing tool, are formed with the same geometry as the fan case. Moreover, the preform take-up spools must have the same geometry as the wrapping mandrel, or the produced fiber preform will not conform to the shape of the mandrel during the preform wrapping process, and wrinkles may form on the composite fan containment case. Wrinkling may reduce the quality of fabricated fan cases. As a result, fabricating conforming fiber preforms may be a difficult and expensive task.